In generators for wind turbines, heat is generated when transferring mechanical energy in electrical energy. The heat is generated in the copper conductors that form the windings of the stator e.g. by Joule losses. The generated heat has to be removed in order to avoid hotspots and insulation wearing.
The stator housing and the attached windings are generally cooled by blowing air inside the stator. In axial end sections of the stator housings the windings protrude and from a half loop. The protruding half loops of the windings form the end windings of the stator windings. The stator windings are cooled by blowing air through the windings, for example in an air gap between rotor and stator or through radial extending ducts of the stator housing. It is also known to attach cooling pipes or hollow copper strains to the stator housing in order to provide a liquid cooling. The conductor sections of the windings that are attached to the stator housing are thereby cooled, but the protruding end windings are only cooled with a lesser efficiency, so that hotspots at the end windings may occur and may lead to damages of the stator winding.